Continual decreasing of feature size of transistors in modern integrated circuits constrains thickness of auxiliary dielectric layers such as barrier layers or etch-stop layers in interconnects because of their relatively high dielectric constant reducing efficiency of low-κ material integration. For example, dielectric materials used today as barrier or etch-stop layers are usually silicon nitride (SiN, κ value of about 7.0) and silicon-carbonitride (SiCN, κ value of about 4.8), dielectric constants which noticeably exceed that of advanced ultra low-κ materials (κ lower than 2.1).
In general, a low-κ dielectric is a material with a small dielectric constant relative to silicon dioxide. Further an ultra-low κ dielectric material is characterized by dielectric constant κ lower than 2.3, more preferably lower than 2.1. Usually the pore size of such a material is between 1 and 5 nm.
Deposition of a thin layer on a porous material without penetrating the pores is often nontrivial and represents a difficult task especially for chemical vapor deposition (CVD) and atomic layer deposition (ALD) techniques which are both using gaseous precursors which can diffuse inside the net of pores thus increasing the effective thickness of the top layer and deteriorating properties of pristine material.